[PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[Li Zhong]

uart_port_check() will return NULL pointer when state->uart_port is
NULL. Check the return value before dereference it to avoid
null-pointer-dereference error because the locking does not guarantee
the return value is not NULL. Here we do not need unlock in the error
handling because the mutex_unlock() is called in callers.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
---

v3: Add the reason why we need to check the NULL value in the commit
message.  The bug is detected by static analysis.

---
 drivers/tty/serial/serial_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 12c87cd201a7..760e177166cf 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -194,6 +194,9 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 	unsigned long page;
 	int retval = 0;
 
+	if (!uport)
+		return -EIO;
+
 	if (uport->type == PORT_UNKNOWN)
 		return 1;
 
@@ -498,6 +501,8 @@ static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
 	struct ktermios *termios;
 	int hw_stopped;
 
+	if (!uport)
+		return;
 	/*
 	 * If we have no tty, termios, or the port does not exist,
 	 * then we can't set the parameters for this port.
@@ -1045,6 +1050,8 @@ static int uart_get_lsr_info(struct tty_struct *tty,
 	struct uart_port *uport = uart_port_check(state);
 	unsigned int result;
 
+	if (!uport)
+		return -EIO;
 	result = uport->ops->tx_empty(uport);
 
 	/*
-- 
2.25.1

Re: [PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[Greg KH]

On Sat, Sep 03, 2022 at 05:45:24PM -0700, Li Zhong wrote:
> uart_port_check() will return NULL pointer when state->uart_port is
> NULL. Check the return value before dereference it to avoid
> null-pointer-dereference error because the locking does not guarantee
> the return value is not NULL. Here we do not need unlock in the error
> handling because the mutex_unlock() is called in callers.
> 
> Signed-off-by: Li Zhong <floridsleeves@gmail.com>
> ---
> 
> v3: Add the reason why we need to check the NULL value in the commit
> message.  The bug is detected by static analysis.

Great, then please follow the rules in
Documentation/process/researcher-guidelines.rst and identify the tools
you are using as well as everything else listed there.

thanks,

greg k-h

Re: [PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[Ilpo Järvinen]

On Sat, 3 Sep 2022, Li Zhong wrote:

> uart_port_check() will return NULL pointer when state->uart_port is
> NULL. Check the return value before dereference it to avoid
> null-pointer-dereference error

> because the locking does not guarantee the return value is not NULL.

Please include also the answer to the "Why it doesn't guarantee?"
question.

In addition, it's expected you'll keep the people who have expressed 
interest in your patch among the receipients for any new version you 
send out. Thank you.

-- 
 i.

> Here we do not need unlock in the error
> handling because the mutex_unlock() is called in callers.
> 
> Signed-off-by: Li Zhong <floridsleeves@gmail.com>
> ---
> 
> v3: Add the reason why we need to check the NULL value in the commit
> message.  The bug is detected by static analysis.
> 
> ---
>  drivers/tty/serial/serial_core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 12c87cd201a7..760e177166cf 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -194,6 +194,9 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
>  	unsigned long page;
>  	int retval = 0;
>  
> +	if (!uport)
> +		return -EIO;
> +
>  	if (uport->type == PORT_UNKNOWN)
>  		return 1;
>  
> @@ -498,6 +501,8 @@ static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
>  	struct ktermios *termios;
>  	int hw_stopped;
>  
> +	if (!uport)
> +		return;
>  	/*
>  	 * If we have no tty, termios, or the port does not exist,
>  	 * then we can't set the parameters for this port.
> @@ -1045,6 +1050,8 @@ static int uart_get_lsr_info(struct tty_struct *tty,
>  	struct uart_port *uport = uart_port_check(state);
>  	unsigned int result;
>  
> +	if (!uport)
> +		return -EIO;
>  	result = uport->ops->tx_empty(uport);
>  
>  	/*
> 

Re: [PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[Greg KH]

On Sun, Aug 28, 2022 at 01:11:59PM -0700, Li Zhong wrote:
> uart_port_check() will return NULL pointer when state->uart_port is
> NULL. Check the return value before dereference it to avoid
> null-pointer-dereference error. Here we do not need unlock in the error
> handling because the mutex_unlock() is called in callers.
> 
> Signed-off-by: Li Zhong <floridsleeves@gmail.com>
> ---
>  drivers/tty/serial/serial_core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 12c87cd201a7..760e177166cf 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -194,6 +194,9 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
>  	unsigned long page;
>  	int retval = 0;
>  
> +	if (!uport)
> +		return -EIO;
> +
>  	if (uport->type == PORT_UNKNOWN)
>  		return 1;
>  
> @@ -498,6 +501,8 @@ static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
>  	struct ktermios *termios;
>  	int hw_stopped;
>  
> +	if (!uport)
> +		return;
>  	/*
>  	 * If we have no tty, termios, or the port does not exist,
>  	 * then we can't set the parameters for this port.
> @@ -1045,6 +1050,8 @@ static int uart_get_lsr_info(struct tty_struct *tty,
>  	struct uart_port *uport = uart_port_check(state);
>  	unsigned int result;
>  
> +	if (!uport)
> +		return -EIO;
>  	result = uport->ops->tx_empty(uport);
>  
>  	/*
> -- 
> 2.25.1
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/SubmittingPatches for what needs to be done
  here to properly describe this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

[PATCH v3] drivers/tty/serial: check the return value of uart_port_check()

[Li Zhong]

uart_port_check() will return NULL pointer when state->uart_port is
NULL. Check the return value before dereference it to avoid
null-pointer-dereference error. Here we do not need unlock in the error
handling because the mutex_unlock() is called in callers.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
---
 drivers/tty/serial/serial_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 12c87cd201a7..760e177166cf 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -194,6 +194,9 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 	unsigned long page;
 	int retval = 0;
 
+	if (!uport)
+		return -EIO;
+
 	if (uport->type == PORT_UNKNOWN)
 		return 1;
 
@@ -498,6 +501,8 @@ static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
 	struct ktermios *termios;
 	int hw_stopped;
 
+	if (!uport)
+		return;
 	/*
 	 * If we have no tty, termios, or the port does not exist,
 	 * then we can't set the parameters for this port.
@@ -1045,6 +1050,8 @@ static int uart_get_lsr_info(struct tty_struct *tty,
 	struct uart_port *uport = uart_port_check(state);
 	unsigned int result;
 
+	if (!uport)
+		return -EIO;
 	result = uport->ops->tx_empty(uport);
 
 	/*
-- 
2.25.1